The present invention generally relates to a modular storage server architecture for retrieving data in response to user access requests. In particular, the invention relates to a server architecture in which data is dynamically distributed over a plurality of disks, a plurality of processors are assigned to particular disks, and data access requests are assigned to particular processors in order to provide good data access performance and server fault tolerance.
A storage server allows users to efficiently retrieve information from large volumes of data stored on a plurality of disks and secondary storage (e.g., magnetic tape or an optical-disk jukebox). For example, a video server is a storage server that accepts user requests to view a particular movie from a video library, retrieves the requested program from disk, and delivers the program to the appropriate user(s). Such a video server is disclosed in U.S. Pat. No. 5,671,377, entitled xe2x80x9cSystem For Supplying Streams Of Data To Multiple Users By Distributing A Data Stream To Multiple Processors And Enabling Each User To Manipulate Supplied Data Streamxe2x80x9d issued to Bleidt et al. on Sep. 23, 1997.
The foregoing storage server employs one or more processors that access data that is stored across an array of disk drives using fault tolerant storage technique such as RAID (Redundant Array of Inexpensive Disks). While such architectures provide uniform non-blocking access to all of the data stored on the disk drives, they do not facilitate a modular architecture. Since data is striped across all of the disk drives in the array, adding or removing disk drives to/from the server requires that all of the data be re-striped across the new set of disk drives. Because the servers are not modular, it is therefore inconvenient to increase or decrease storage capacity by adding or removing disk drives.
There is therefore a need in the art for a storage server architecture that is modular and can acceptably resolve content blocking issues.
The disadvantages associated with the prior art are overcome by the present invention of a server comprising a plurality of modules, each of which contains a single processor and a cluster of, for example, 16 disk drives, and a host controller that communicates with and assigns data requests to each of the modules. Data is written to the disk drives by striping the data across the 16-disk drive cluster of a single module according to a RAID-5 protocol, with parity and spares distributed amongst the disk drives in the cluster.
The architecture of the present invention employs dynamic data management methods, which determine whether data should reside on disk or secondary storage, on which disk drives data should be stored, and how data should be replicated and/or migrated to new disk drives based on observed user access patterns. These methods also migrate popular data to faster disk tracks to reduce average access time and thus improve performance.
User access requests are assigned to modules based on the data stored at each module, and each module""s current load (the number of requests waiting to be serviced). If the requested data is not on a disk drive, the data is retrieved from secondary storage, and may be stored on the disk drives for rapid subsequent access. When a requested data item on the disk drive is replicated, load balancing is performed by assigning the request to the module holding the data with the lowest load. In addition, user access requests waiting to retrieve replicated data may be dynamically and seamlessly migrated to another module based on changes in module loads.